(1) Field of the Invention
The present invention relates to a multi-parameter fluid flow characteristic sensor and more particularly to a measuring device for determining fluctuating wall pressure and fluctuating wall shear stress simultaneously at a solid wall bounding a turbulent fluid flow.
(2) Description of the Prior Art
In principle, simultaneous measurement of fluctuating wall pressure and fluctuating wall shear stress in a turbulent boundary layer at a single spatial location is attainable in restricted laboratory situations by using a flush mounted piezoelectric pressure transducer and a Laser Doppler Velocimeter (LDV). FIG. 1 shows a typical turbulent boundary layer velocity profile and the viscous sublayer region thereof. In practice, the laser light measuring volume of the LDV must be optically positioned directly above the face of the piezoelectric transducer. The fluctuating streamwise velocity is then measured, and the fluctuating shear stress in the fluid at the wall hereinafter referred to as the fluctuating wall shear stress may then be determined. This measurement may be made provided that the diameter of the measurement volume of the LDV is at least an order of magnitude smaller than the thickness of the viscous sublayer region of the turbulent boundary layer. The viscous sublayer, as shown in FIG. 1, is a very thin region that extends from the wall, in a direction normal to the wall, a distance proportional to the mean wall shear stress. Due to the thinness of the viscous sublayer in water flow laboratory testing facilities however, the above criteria can very rarely be met. In addition, the principle of operation of the LDV necessitates seeding the fluid medium with silicon carbide particles or the like in order to obtain required data rates. Attaining the required density of the seed particles within the viscous sublayer in water is technically very difficult. Measurements of fluctuating wall pressure are frequently made on scale models and full size vessels at Naval testing sites both at sea and in lakes. The use of an LDV is physically impossible for these vessel type tests due to optical constraints, size limitations, and environmental restrictions. An additional disadvantage of the LDV is that it is very costly.